The pilot design in uplink (UL) multiple antenna systems presents a very difficult problem and the pilot design must accommodate a number of different considerations. From the perspective of demodulation performance, it is best to concentrate the pilot power exactly to the frequency and time resources used for data. This is referred to as in-band pilot. From the perspective of being able to schedule users onto different frequencies, it is beneficial to transmit a wider band pilot. This is referred to as out-band pilot.
For a closed loop transmission from multiple antennas, the pilot design must solve the same problem as for channel dependent scheduling. That is to design a pilot transmission, which provides robust data demodulation, while simultaneously providing the possibility to calculate Channel Quality Indicator/Frequency correction Burst (CQI/FB) that is needed to align the transmissions from the multiple antennas at the receiver.
The Long Term Evolution (LTE) Technical report (3GPP TR25.814 v1.0.3, Rel7), suggests and only states that the pilots in uplink (UL) may be multiplexed in frequency division multiplex (FDM) or time division multiplex (TDM) or code division multiplex (CDM) or the combination of them, and that the pilot signals are transmitted within two short blocks. The multiplexing mentioned in the prior art means multiplexing between different pilot signals for example, from multiple user equipments (UE's). The multiplexing methods mentioned in the LTE technical report do not refer to or suggest multiplexing between antenna-specific and beam-specific pilots. Although in-band and out-of band solutions are known as well as antenna-specific pilots and beam-specific pilots, it is not known to combine the two. According to the inventors' knowledge and understanding, the multiplexing method between antenna-specific and beam-specific pilots does not exist in the LTE system. In LTE, the term “antenna-specific” pilot is also known as “common” pilot and the term “beam-specific” pilot is also known as “dedicated” pilot.
It is desirable to provide a pilot design transmission in uplink (UL) in multiple antenna systems by combining the antenna-specific and beam-specific pilots.